The preparation of biological specimens is performed, for example, for the purpose of electron-microscope examination. Microwaves are used in this context to excite and accelerate the fixation, substitution, infiltration, and polymerization processes. The overall time for preparation processes can thereby be greatly reduced.
A microwave-assisted device for extracting substances from a starting material is described in U.S. Pat. No. 5,620,659. A number of specimen holders are mounted in a carousel-like turntable and placed, as a whole, in a multimode chamber. Conduits from each specimen holder lead into a collection container that can additionally be pumped down in order to avoid contamination of the multimode chamber with escaped gases.
U.S. Pat. No. 6,875,583 discloses a device for rapid microwave-assisted fixation of tissue. Biological prepared samples are positioned, in a formalin solution serving as a fixing agent, in the microwave field of a multimode chamber. The microwave power output is controllable. The temperature is controlled by pump-circulating and cooling the fixing solution outside the microwave field.
The pump-circulating and cooling of reagents during the processing of biological samples has the disadvantage that reagent replacement entails considerable complexity. Valves, pumps, and reservoir and waste containers must be provided. In U.S. Pat. No. 6,875,583 the use of the disclosed invention is therefore limited to one specific process step. A relatively high consumption of chemicals is also associated with an arrangement of this kind, since not only the process vessel but additionally the entire cooling circuit must be filled. The replacement and replenishment of reagents must also encompass washing steps for the cooling circuit.
Multimode microwave chambers, i.e. chambers such as a household microwave oven having relative large chamber dimensions, exhibit large local inhomogeneities in microwave intensity (so-called “hot spots” and “cold spots”). Apparatuses for homogenizing the microwave field are therefore necessary in order to create defined and reproducible process conditions.
U.S. Pat. No. 4,681,740 and U.S. Pat. No. 5,459,302 disclose the arrangement of reaction vessels in a microwave field that is constituted in a waveguide. The receptacle for a reaction vessel is embodied so that the lower end of the vessel is located in the wave field, and the upper end projects out of the waveguide. The projecting part is surrounded by a tube that prevents the emergence of microwaves. The temperature of the reaction vessel can be monitored by way of a pyrometer.
U.S. Pat. Nos. 6,753,517, 6,917,023, and 6,744,024 disclose devices for microwave-assisted chemical synthesis. The reagents are located in a microwave-transparent reaction vessel that is positioned inside the internal cavity of a microwave resonator shaped like a cylindrical ring; the specimen is not, however, located in the actual waveguide that annularly surrounds the cavity. Apertures in the inner waveguide wall cause microwave radiation to travel to the reaction vessel. A comparatively homogeneous distribution of the microwave radiation field over the region in which the reaction proceeds is thereby achieved, but this arrangement requires additional complex sealing of the microwave radiation toward the outside. The temperature in the reaction vessel is monitored by a sensor, and is controlled by regulating the microwave power output or by cooling the outer shell of the reaction container with the aid of a flow of gas or liquid.
The above-described methods for microwave-assisted preparation require a manual replacement of the reagents when the specimens are to be processed sequentially in different liquids, and are therefore labor-intensive. In conventional tissue processors, specimen processing takes from several hours (e.g. 24 hours) to days, depending on the protocol. Only after this long waiting time are the specimens therefore available for examinations in the electron microscope.
It is additionally known, in the context of the processing of specimens in a sequence of liquids, to place said liquids in a turntable carrier (a so-called carousel), and for the specimen to be immersed sequentially, in a process device, into the liquids present in the carousel. A usual procedure for this is to rotate the carousel beneath the specimen so that the liquid to be utilized becomes positioned below the specimen, and then the entire carousel is raised until the specimen is immersed. The desired process step can then take place, additionally (if necessary) with the use of a heating system or like. The carousel is then lowered, rotated further, and so on. This procedure is of little advantage in connection with microwave radiation, since a carousel is too bulky for introduction into a waveguide, or the entire carousel would need to be placed into a waveguide (as in U.S. Pat. No. 5,620,659), although the liquids not being used would also be affected by the microwave radiation.